My itr had a strange voltage issue, i had no clue if it is related to the alternator...
Well, the problem is when it is under high speed (roughly over 120km/hr) and high rpm (like over 7k rpm), if it is under braking, all the lights (head lights, cluster lights) will bright up for few seconds. Also, CEL and battery light will come on @ the same time...and the voltage read up to 15.9 v (from the power fc commander)

However, it won't happen if it is not under high rpm. Normal driving, the car runs fines.
I have checked the grounding and most of the connection between battery and wiring, everything seems fine to me. The battery is still good. so What's wrong with my itr?! what it can be wrong??? alternator??

 

I never really heard of a voltage spike, usually its loss of voltage and the lights will dim at higher RPM. My car used to do that but mysteriously stopped lol.

What does the battery/alternator read at idle? Measure it with a multimeter. I wonder where the Power FC is picking up the voltage source from? the battery or the alternator? Id guess the alternator so maybe try another alternator if possible.

 

the battery/alternator read around 13.9 to 14.1 v @ idle from power fc commander
since the power fc replaces the stock ecu, i guess it is from alternator. (my apexi turbo pick up the voltage signal from the one of the ecu harness but it doesn't response as good as the commander tho...)

I will check the alternator and battery and see if that's the problem